One thing I've always wondered when I install suspension is how tight should the top perch bolts be tightened? Since the strut tower is threaded, what if the two sides are uneven? Couldn't that make the ride height different on both sides?

I've attached a pic (thanks Speedtrap for the borrowed pic). Say for instance the top nut is tightened to 1 on one side and 2 on the other. Won't the ride height be different on both sides? Or is the general rule of thumb to make both sides about even?

Also ... if you tighten both sides to position 1 or both to position 2 won't that yield different ride heights? That's a good inch right there. I know those positions are extreme ends of the threads, but I'm just trying to make my point here.

If everything in both illustrations are exactly the same except the nut position, once you lower the car the spring will compress to the same steady state height regardless of either setup.

The ride height will be determined by the spring itself and the shock/strut base position (the "sleeve" where the bottom of the strut is inserted) as previously explained.

Ok cool I guess that makes sense, but how about in the extreme case if the uninstalled strut has a top mount that is compressing the spring even more than the normal weight of the car would when it's installed? This would the car to be even lower right?

Ok cool I guess that makes sense, but how about in the extreme case if the uninstalled strut has a top mount that is compressing the spring even more than the normal weight of the car would when it's installed? This would the car to be even lower right?

... then we would not be talking about the same setup, as one strut will compress the spring more than the original strut, something like a coilover vs. standard strut.

The top of the spring sits on a spring perch that's mounted to a bearing that's bolted (with three small bolts) upside-down inside the fender. The bottom of the spring sits on a perch that's clamped to the top of the damper body. The spring sits between these two perches.

The nut you are wondering about in the original post just keeps the damper rod in place - too loose and it will rattle, too tight and it will damage the threads and maybe the rubber bushing it sits in the middle of. Other than that, it has no effect on the ride height.

You'll feel when the nut makes contact, sandwiching the washer assembly. IIRC, a 10mm socket fits over the top of the shock shaft. I used a ratchet on that and an open-end box wrench on the nut and squeezed to an approximated 18-20ft-lb. RealOEM doesn't have torque specs so I assumed this based on previous M3 specs. You can always torque the nut down after the assemblies are installed on the car. This may even be easier since the shaft shouldn't spin with the car on the ground under the spring's tension.

I tightened this up today being that I had that clunking sound. However, I did not tighten it with the torque measurer being that the dealer wanted me to leave the car there for the day for something that would take 5 minutes. So I took it to my mechaninc, he tightened it down with a wrench and the sound is gone. Didnt turn too much but there was deff some room.

The bearing rides on the shaft collar. The tightening of the nut serves to hold the strut in position in the collar. It does nothing to the ride height unless your car sits with the shocks fully extended, which it doesn't...

I'm not even sure the torque number is correct. I'll have to look at the manual to be sure.

The bearing rides on the shaft collar. The tightening of the nut serves to hold the strut in position in the collar. It does nothing to the ride height unless your car sits with the shocks fully extended, which it doesn't...

I'm not even sure the torque number is correct. I'll have to look at the manual to be sure.

I was just referring to tightening the nut to the shock. My friend and I installed my springs after removing my sleeve overs. The position of the nut sat at a different height when my s/o were installed. We did not tighten the nut that much once the springs were installed to mimic the look of the s/o. I received the clunking noise when driving as well but after reading this post, I just tightened the 2 strut nuts and the clunking went away. I guess it had to do with different spring rates. Either way, the car rides like a champ now!

I was just referring to tightening the nut to the shock. My friend and I installed my springs after removing my sleeve overs. The position of the nut sat at a different height when my s/o were installed. We did not tighten the nut that much once the springs were installed to mimic the look of the s/o. I received the clunking noise when driving as well but after reading this post, I just tightened the 2 strut nuts and the clunking went away. I guess it had to do with different spring rates. Either way, the car rides like a champ now!

Great! You do have to tighten that nut down or the shaft will thunk around (up and down motion) in the strut bearing. I've had them loosen up before in my old race car (that's what I get for re-using nylock nuts).

If you ever have to do this again, make sure you don't spin the shaft of the strut when you are tightening the nut. In some shocks this can damage the valve body. Not saying you did this time, but sometimes people get carried away tightening things!